Figure 4

Morphology and mitochondrial β-oxidation are altered in TXNIP-KO mice during fasting. The morphology and the expression of β-oxidation-related and mitochondrial fission–fusion related genes, especially in the fasted state, were evaluated by TEM and RT-qPCR, respectively. (a) Top row: Mitochondrial size and number were compared. The size of mitochondria was small and the number of mitochondria increased in TXNIP-KO mice during fasting, although there appeared no obvious difference in the number of mitochondria between the both type of mice. Bottom row: Mitochondrial structures were compared. Although no obvious difference was found in the structure of cristae between WT and TXNIP-KO mice in the fed state, mitochondria were swollen and lacked cristae, and anomalously broken mitochondria (arrow head) were also observed in TXNIP-KO mice in the fasted state (scale bar = 500 nm). (b) The areas indicated by the boxes in figure (a) are enlarged. Compared with WT mice, the irregularity in the outer membrane was found in TXNIP-KO mice during fed state and this membrane irregularities were more evident during the fasted state. (c,d) Ten foci from each group were examined, and the mitochondrial size and number were quantitated. Mitochondrial size was statistically smaller in the liver of TXNIP-KO mice during the fed state, and the difference became more prominent during the fasted state, despite the fact that the number of mitochondria in the fasted state was not different between WT and TXNIP-KO mice. (e) Differences in the expression of β-oxidation-related genes or proteins between WT and TXNIP-KO mice. Overall, β-oxidation-related gene expression was upregulated in WT mice during the fasted state, but this change was not observed in TXNIP-KO mice. Expression of β-oxidation-related genes (Ppara, Cpta, Acadvl, and Acadl) was significantly higher in WT mice than in TXNIP-KO mice during the fasted state, indicating impaired β-oxidation in TXNIP-KO mice during the fasted state. (f) Gene expression of molecules related to mitochondrial fission and fusion (Dnm1l, Fis1, Mfn1, Mfn2) was examined. The expression of these molecules was upregulated in fasted state in WT mice, but this change was not found in TXNIP-KO mice. *p < 0.05. **p < 0.01 (in each group, six mice were used for RT-qPCR). TEM transmission electron microscopy, TXNIP thioredoxin-interacting protein, WT wild-type mice, KO knockout mice, PPARα peroxisome proliferator-activated receptor-α, CPT1 carnitine palmitoyltransferase 1, ACADVL acyl-CoA dehydrogenase very long chain, ACADL acyl-CoA dehydrogenase long chain.